Writing a 100% cycle accurate c64 emulator is a bit pointless, you might as well just port vice. Some of the nastiest tricks you can do on the c64 are used by a couple of demos that were written after the c64 died.

An emulator good enough for most games is probably worth doing for pocket pc or a gp32, although I'd be more interested in modding a c64dtv into a handheld case.

smf